ACE Exploring Atmosphere and Climate of the Earth Using GPS, GALILEO, and LEO-LEO Occultations Per H

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ACEExploring Atmosphere and Climateof the
EarthUsingGPS, GALILEO, and LEO-LEO
OccultationsPer Høeg (AIR/DMI)Gottfried
Kirchengast (IGAM/UG)
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Objectives

• Climate
• Monitoring global long-term variations in the
  climate and the forcings of the atmosphere system
  giving rise to trends
• Atmosphere
• Observe and analyze globally the physical
  condition and state of the atmosphere of the
  Earth to improve predictions of future state
• Space Weather
• Monitoring and modeling of ionosphere and
  plasmasphere electron density structures

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Primary Issue of Concern Climate Change

• Increasing evidence exists that the Earths
  climate is currently changing (e.g., IPCC 2001
  Report). The changes are most pronounced in the
  most variable component of the Earth system, the
  atmosphere.
• Key indicators
• Humidity and temperature in the troposphere
  tend to increase
• Stratospheric temperatures tend to decrease
• Stratospheric humidity tend to increase with
  drastic changes in the radiation
• It is likely that these changes are associated
  with human-induced
• increases of greenhouse gas concentrations
  in the atmosphere.
• Natural variability of the climate system
  complicates the picture,
• rendering proper understanding of climate
  change very challenging.

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Variability of Atmospheric Water Vapor
Radiosonde Humidity Profile (Kauai, Hawaii, 1 Oct
2000, 12UTC)
Latitude-Height Slice of Humidity based on ECMWF
analysis (15 Sep 1999, 12UTC, 79W)
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Water Vapor Variability
Column Water Vapor Monthly Map January 1994
Column Water Vapor Monthly Map July 1994
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Greenhouse Gas Emissionsand Temperature Change
Projections
b) Corresponding near surface temperature
change projections
a) CO2 emission paths for several representative
IPCC scenarios
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Present Observations
Global tropospheric and surface temperature data
from different sources (MSU MSU satellite data,
UKMO radiosonde-based data, Surface surface
data) Inset difference between surface and
radiosonde data
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Scientific Objectives

• Major goal
• Monitor and describe variations and changes in
  the global atmospheric temperature and water
  vapor distribution
• Assess climate changes caused by mass field
  changes and atmosphere dynamics.
• Main objectives
• To establish highly accurate (lt 0.025 g/kg and lt
  3 in specific humidity) and vertically resolved
  (lt 1 km) global climatology of water vapor in the
  troposphere
• To establish a highly accurate (lt 0.2 K) and
  vertically resolved (1 km) global climatology of
  temperature in the troposphere and the
  stratosphere
• To perform research on climate variability and
  climate change together with research in improved
  atmospheric models as well as advancements in
  NWP
• To study troposphere structures in polar and
  equatorial regions
• To support analysis and validation of data from
  other space missions
• To demonstrate a new and novel active atmospheric
  sounding technique with the CALL instrument
• To enhance the European observational capability
  for improved contribution to the international
  GCOS initiative.
• Advances in atmosphere physics and climate change
  processes
• Global climate warming and increased averaged
  atmospheric water vapor levels
• Tropical heat and mass exchange with
  extra-tropical regions
• Transport across subtropical mixing barriers,
  relevant for information on the lifetime of
  greenhouse gases
• Stratospheric winds and temperatures and
  atmospheric wave phenomena
• Polar front dynamics and mass exchange together
  with tropospheric water vapor feedback on climate
  stability

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Satellite Constellation

• 4 micro-satellites
• Mass 130 kg
• Power 80 W
• Stable two-plane constellation in 90 degrees
  inclination
• In each plane, counter-rotating orbits with 2
  satellites - for optimizing quality of
  measurements
• Two altitudes
• Heights 650 km and 850 km to optimize spatial
  distribution of occultations
• Orbital local time drift
• To optimize the temporal and local time
  distribution of occultations
• Instruments
• L-band GPS/GALILEO precision receiver
• X/K-band LEO-LEO precision transmitter and
  receiver (2 of each)

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Why is measurements ofatmospheric water vapor
important ?

• Indicator of climate change
• Strongest greenhouse gas
• Climate positive/negative feedback
• Energy reservoir
• Impact/feedback on global wind system changes and
  general atmosphere dynamics
• Hydrologic cycle
• Highly variable (time and space)

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Global Temperature Deviations
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Forcing residuals in atmospheric models

• Estimation of the residual (R) requires
  availability of high quality observed data.
• Forcing residuals can be used to
• identify tendency errors in the differential
  equations of atmospheric models
• detect temporal variations in external forcing of
  the atmosphere.

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Weak nudging towards the re-analyses

Data assimilation via nudging
Discretization in time (assimilation in spectral
space)
Forcing residual is approximated by the last
fraction
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The ACE Experiment
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GRAS Temperature Retrieval
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Processing Steps for Water Vapor Retrievals
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GRAS Requirements
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Absorption at X/K-band frequencies
Frequencies 10.0-11.5 GHz 17.2-17.3
GHz 22.5-23.5 GHz
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Absorption
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CALL Temperature and Humidity Retrieval
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CALLTemperatureand HumidityRequirements
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Weekly Profile Coverage
Weekly latitudinal distribution of occultations.
Longitudinal variations still exist in the seven
days simulation. Part of the spread in the plot
is due to this effect. For the 500 x 500 km
cells the following statistics can be
calculated Average number of occultations in a
cell 22.49 Standard deviation 10.36
Average time difference (min) between profiles in
each cell as function of latitude. The simulation
covers a whole week of data. Average time
difference between the occultations 482 min
8h 2min Standard deviation 216 min 3h
36min
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Global Distribution of Occultations
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Distribution of NWP Radiosonde Observations
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Global Distribution of LEO-LEO Occultations
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Global Humidity Fields
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• Launch
• 2006/2007
• Mission lifetime
• 5 years (2006 2012)